The invention relates to a rolling-contact bearing for use in a shaft journal of a heated roll or calender.
Rolling-contact bearings in heated rolls or calenders, used, e.g. for the production of paper, plastics, textiles or wood, are subjected to high thermal loads because there is a continuous flow of heat transfer medium, e.g. superheated steam or hot oil for drying the endless webs, flowing through the shaft. Accordingly, the inner race of the rolling-contact bearing is always warmer during shaft operation than the outer race, which is seated in a housing. To reduce the flow of heat from the shaft journal to the inner race, a wide variety of different insulating measures have been tried.
The SKF Kugellager Magazine (number 233, Dd 7391 88-12 Reg. 07771, page 2 ff; number 238, Dd 7531 91-12 Reg. 07771 page 25 ff; number 239 Dd 7617 92-05 Reg. 07771, page 24 ff) and the SKF Handbook 4200T Bearings for Paper Machines, Reg. 861 2 3000 1993-02, page 56 ff describe the problems of this bearing location in great detail. Attention is drawn, in particular, to the need for insulation in the shaft journal. These publications are evidence of years of intense preoccupation with this bearing location. Additional insulation between the rolling-contact bearing and the shaft journal is not described in this context.
In DE 44 28 419 A1, a clamping structure is provided between the shaft journal and the inner race of the rolling-contact bearing to insulate and compensate for the temperature of the bearing. This clamping structure is subjected to axial force by a thrust device. The disadvantage of this solution is that it involves a very high outlay and cannot be retrofitted without reworking the shaft journal.
It is therefore the object of the invention to provide a rolling-contact bearing for a heated shaft journal, which bearing, on the one hand, has better thermal insulation and, on the other hand, can be installed in the vicinity of the bearing location without additional modifications.
According to the invention, this object is achieved by a rolling-contact bearing with an inner and an outer race and rolling elements between the races. The inner race has an inner bore received on the shaft journal and the inner bore of the inner race is provided with a ceramic layer for reducing the heat transfer from the shaft journal through the ceramic layer to the rolling-contact bearing. In addition, the rolling-contact bearing may be secured on the shaft by securing elements applied at one lateral side of the inner race. The ceramic layer may be provided on the inner race at the lateral side in contact with the securing element, as the securing element is on the shaft journal, as well.
The following advantages are obtained for rolling-contact bearings by coating the inner race with ceramic in accordance with the invention:
The entire rolling-contact bearing is at a lower bearing temperature.
The difference between the operating temperatures of the inner race and of the outer race is reduced. This also reduced the problems associated with the bearing air of the rolling-contact bearing in the various operating states.
There is less mixed friction in the rolling-contact bearing so that the rolling-contact bearing therefore has a longer life.
The life of the lubricating oil used in the bearing increases and the volume flow of lubricating oil through the rolling-contact bearing can be reduced.
Another advantage of these coated rolling-contact bearing is that they can be used without modifications to the surrounding parts. This is particularly important for using these new coated rolling-contact bearings within existing systems without additional expenditure.
The ceramic layer preferably contains at least 90% zirconium oxide ZrO2, while the remainder is predominantly yttrium oxide Y2O3. An adhesive layer is applied between the inner race and the ceramic layer and it is composed of chromium and nickel. One example of the composition of the coating is a {fraction (1/10)}-mm adhesive layer and a {fraction (9/10)}-mm ceramic layer.
The thickness of the coating must be taken into account in the dimensioning when producing the inner races to ensure that the rolling-contact bearings have their standardized outside dimensions after coating in order to enable the coated rolling-contact bearings to be used without problems in locations where uncoated rolling-contact bearings had previously been used.
The inside and/or outside diameters or surfaces and end contact surfaces of the withdrawal, clamping and taper sleeves are also provided with the above ceramic layer. For rolling-contact bearings which are mounted on a shaft and which use withdrawal sleeves or clamping sleeves, this significantly enhances the insulating effect because several surfaces between the shaft journal and the inner race of the rolling-contact bearing are coated. This further reduces the flow of heat introduced into the rolling-contact bearing via the inner race.